Disaster in or failure of a storage apparatus causes loss of data stored in the storage apparatus and stops service. In order to recover data even if such loss of data occurs, backup is necessarily performed by duplicating data in another storage apparatus through remote copying.
In order to suppress loss of data to a minimum at the time of failure, the speed of processes is required to be as high as possible in performing such duplication of data. In addition, competition occurs between a data duplication request such as backup and an input-output request from a host apparatus to a storage apparatus, degrading both host I/O performance and backup performance.
A method for avoiding competition between input-output performance of host I/O and backup is disclosed in PTL 1. In a manner of creating a log according to a data update request from a host apparatus, an additional log that is different from a normal log is created on a disk in addition to creating a normal log on the disk. In the disclosure, the additional log is separated at the time of obtaining a backup while a log continues to be created as a normal log. The additional log separated is set to be read-only, and backup data is read from the additional log. This allows a backup process to be performed without competition between backup and host I/O to the normal log.